Last week, DVN published a Request For Comment from the lighting community at large regarding the effects of heat on plastic materials in LED headlamps. Feedback received tended towards the view from lamp set makers that there is no problem evident at this time, as long as materials are selected and applied thoughtfully. Koito’s Masaru Sasaki, for example, a key engineer on the supplier’s LED headlamp for the Lexus LS600hL, said :
“I never heard such problem for transparent plastics in LED headlamps (…) Epoxy resin shows little degradation for red LEDs, but the problem appeared after blue and white LEDs were introduced, because the energy of single photon is higher for blue light compared to red. Epoxy resin also degrades by high temperature, so the degradation is accelerated by combination of both high temperature and high energy photons of blue light. Therefore, we have developed a glass covered LED to remove any degradable materials. The only remained polymer was carefully chosen from photon-resistant polymer to bind phosphor powder. We should be very careful to choose material for LED package (…) Bad design or improper selection of material may cause some trouble [in the long run] but this is nothing special for LEDs.”
Sasaki’s comments, particularly his final remark, strike directly at a key reason why the US-based Society of Automotive Engineers has formed a task force to examine the matter and eventually issue design guidelines. Materials suppliers say they have customers specifying very costly materials — such as one that costs $45 (USD) per kilogram, more than twice the cost of a less-exotic alternative—because there is no technical standard or endurance test protocol for materials that may degrade in the long-term service of a headlamp supposed to last the life of the car. There are some engineers who think the problem is entirely due to heat, some who say it’s due to short-wavelength visible light, and others who point to UV exposure as the initiating factor in a “death spiral” whereby slight degradation worsens exponentially with continued operation of the lamp. Thank you, Mr. Sasaki, for your helpful remarks. Other community members with thoughts on the matter are encouraged to take a moment to send them in .
